What does Luke 22:58 mean?

Peter is in the courtyard of the high priest Caiaphas. Earlier, a servant girl accused him of being one of Jesus' disciples. Sitting near the fire, surrounded by some of the guards and servants who had arrested Jesus, Peter lied and claimed he was not (Luke 22:54–57).

Since His arrest, Jesus has been the defendant in an illegal trial with very prejudiced judges. Priests, Pharisees, scribes, and elders have been trying to get Jesus to admit that He teaches heresy. When He challenges them to produce witnesses, they strike Him (John 18:19–22). Witnesses are called but even when they lie, their testimony doesn't agree (Mark 14:55–59). All this is going on as Peter denies that he follows Jesus.

The accounts of Peter's denials get confusing. This is the second that Matthew, Mark, and Luke record.

Matthew's account says,

And when he went out to the entrance, another servant girl saw him, and she said to the bystanders, "This man was with Jesus of Nazareth." And again he denied it with an oath: "I do not know the man." (Matthew 26:71–72)

Mark's says,

And the servant girl saw him and began again to say to the bystanders, "This man is one of them." But again he denied it. (Mark 14:69–70)

In Luke, Peter's response is "Man, I am not!" Peter isn't speaking to the servant girl; he's speaking to one of the guards or servants who heard the girl and has indicated interest in her accusation.